Silicon oxycarbide, growth method of silicon oxycarbide layer, semiconductor device and manufacture method for semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device includes the steps of: preparing an underlying structure having a silicon carbide layer covering a copper wiring, and growing silicon oxycarbide on the underlying structure by vapor deposition using, as source gas, tetramethylcyclotetrasiloxane, carbon dioxide gas and oxygen gas, a flow rate of said oxygen gas being at most 3% of a flow rate of the carbon dioxide gas. The surface of the silicon carbide layer of the underlying structure may be treated with a plasma of weak oxidizing gas which contains oxygen and has a molecular weight larger than that of O 2  to bring the surface more hydrophilic. Film peel-off and cracks in the interlayer insulating layer decrease.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 13/493,244 filed on Jun. 11, 2012, which is a divisional applicationof U.S. application Ser. No. 12/314,036 filed on Dec. 3, 2008, now U.S.Pat. No. 8,349,722, which is a divisional application of U.S.application Ser. No. 11/206,955 filed on Aug. 19, 2005, now U.S. Pat.No. 7,485,570, which is a divisional application of U.S. applicationSer. No. 10/694,826 filed Oct. 29, 2003, now U.S. Pat. No. 6,949,830,which was based on and claimed priority to Japanese Patent ApplicationNo. 2002-315900 filed on Oct. 30, 2002, the entire contents of whichbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

A) Field of the Invention

The present invention relates generally to a low dielectric constantinsulator having a low specific dielectric constant, a method of growinga low dielectric constant insulating layer, a semiconductor devicehaving a low dielectric constant insulating layer, and a method ofmanufacturing a semiconductor device having a low dielectric constantinsulating layer. The invention relates specifically to a low dielectricconstant insulator suitable for use with a semiconductor integratedcircuit having multi-layer wirings, a method of growing a low dielectricconstant insulating layer, a semiconductor device having multi-layerwirings and low dielectric constant insulators, and a method ofmanufacturing such a semiconductor device.

B) Description of the Related Art

Semiconductor integrated circuit devices are becoming highly integrated,and there is the tendency that the scale of wirings of each deviceincreases one generation after another. As the wiring scale becomeslarge, the number of wiring layers increases so that a multi-layerwiring structure is adopted. High integration of a semiconductorintegrated circuit device results in a narrow wiring space.

There is the tendency that the wiring space is narrowest at lower levelwiring layers and broadens toward upper level wiring layers. Many oflower level wirings are used for transmitting signals, whereas many ofupper level wirings are used for power source lines. Because of thischaracteristic difference, the conditions required for multi-layerwirings are not the same.

A transmission speed of a signal in a wiring is governed by wiringresistance and wiring parasitic capacitance. It is desired for a highspeed operation to lower a wiring resistance and reduce a wiringparasitic capacitance.

In order to lower a wiring resistance, Cu wirings are used nowadays inplace of Al wirings. It is difficult to use wiring material having aresistivity lower than that of Cu. As the reduction in a wiringresistance reaches near its limit, it becomes necessary to reduce awiring parasitic capacitance. When Cu wirings are used, a diffusionpreventive film of SiN, SiC or the like is formed covering each Cuwiring in order to prevent oxidation and diffusion of Cu.

A parasitic capacitance between wirings increases if the wiring spacebecomes narrow assuming the same wiring thickness. The influence of aparasitic capacitance upon a device operation speed is small if thedevice has a wiring space of 1 μm or broader, whereas this influencebecomes large if the device has a wiring space of 0.5 μm or narrower. Itcan be expected that if a device has a wiring space of 0.2 μm ornarrower, the parasitic capacitance greatly influences the deviceoperation speed.

The parasitic capacitance between wirings can be reduced if the wiringthickness is made thin and the confronting area of adjacent wirings ismade small. However, as the wiring thickness is made thin, the wiringresistance increases so that the operation speed as a whole cannot beimproved.

The most effective means for reducing the wiring parasitic capacitanceis to make an insulating layer between wirings have a low dielectricconstant. Insulating materials having a lower specific dielectricconstant have been used in place of silicon oxide (USG) having aspecific dielectric constant of about 4.1, P-doped silicon oxide (PSG)and B—P-doped silicon oxide (BPSG).

Other materials now in use include: organic insulating materials havinga very low specific dielectric constant (such as SiLK (registeredtrademark) and FLARE (registered trademark)); and porous materials suchas porous silicon oxide. These materials have characteristics largelydifferent from those of silicon oxide and are difficult to be used asthe material of an interlayer insulating film for multi-layer wiringsbecause of their mechanical strength, reliability and the like. Thesematerials are therefore used mainly for lower level wiring layers.

Silicon oxycarbide (SiOC) has been paid attention as another insulatingmaterial having a low specific dielectric constant. A vapor-grownsilicon oxycarbide film available from Novellus Systems, Inc., calledCORAL (registered trademark), is manufactured at a deposition speed ofabout 1000 to 1200 nm/min by plasma enhanced chemical vapor deposition(CVD) under the conditions of source gas oftetramethylcyclotetrasiloxane (TMCTS), oxygen (O₂) and carbon dioxide(CO₂), a flow rate TMCTS:O₂:CO₂=5:250:5000 (ml/min, sccm), a gaspressure of 4 torr, an HF (13.56 MHz) power of 600 W and an LF (1 MHz orlower) power of 400 W.

This insulating material called CORAL has Si—O—C as its main skeletonand a specific dielectric constant of 2.9 which is considerably lowerthan that of silicon oxide. This insulating material is promising as aninterlayer insulating layer material for multi-layer wirings.

It has been proposed that a silicon oxycarbide layer is used partiallyas a hard mask layer and thereafter the silicon oxycarbide layer is leftas a portion of an interlayer insulating film having a low dielectricconstant (refer to Japanese Patent Laid-open Publication No.2003-218109, family of U.S. patent application Ser. No. 10/053,288 filedon Jan. 17, 2002).

A low specific dielectric constant material is generally has lowadhesion to, for example, an underlying layer formed as a diffusionpreventive film for Cu. If the number of wiring layers is increased byusing interlayer insulating films having low adhesion, a film peel-offoccurs at the interface to the underlying layer.

It is desired that the multi-layer wiring structure uses a lamination ofa plurality of low dielectric constant insulating layers havingdifferent thermal expansion coefficients. The material having a lowspecific dielectric constant has generally the tendency of a low densityand a low mechanical strength. If there exists a mismatch of a thermalcoefficient between interlayer insulating layers, a large stress isgenerated at the interface so that cracks may be formed in theinsulating layer having a low relative dielectric factor.

SUMMARY OF THE INVENTION

An object of this invention is to prevent peel-off and cracks ofinterlayer insulating layers for multi-layer wirings.

Another object of the invention is to provide insulating material havinga low dielectric constant suitable for use as the material ofmulti-layer wirings of a semiconductor device.

Still another object of the invention is to provide a method of growinga low dielectric constant insulating layer on an underlying layer.

Further object of the invention is to provide a semiconductor device ofhigh reliability having multi-layer wirings with low dielectric constantinsulating material, and a method of manufacturing such a semiconductordevice.

According to one aspect of the present invention, there is providedsilicon oxycarbide which contains hydrogen and has a carbon content ofat least about 18 at % and a specific dielectric constant of at mostabout 3.1.

According to another aspect of the present invention, there is providedsilicon oxycarbide whose hydrogen content is at most 30 at % and whosespecific dielectric constant is at most about 3.1.

According to another aspect of the present invention, there is provideda method of growing a silicon oxycarbide layer comprising the steps of:preparing an underlying layer; and growing a silicon oxycarbide layer onthe underlying layer by vapor deposition using, as source gas,tetramethylcyclotetrasiloxane, carbon dioxide gas and oxygen gas, a flowrate of said oxygen gas being at most 3% of a flow rate of the carbondioxide gas.

According to another aspect of the present invention, there is provideda semiconductor device comprising: a semiconductor substrate; a copperwiring formed above the semiconductor substrate; a silicon carbide layercovering the copper wiring; and a first silicon oxycarbide layercovering the silicon carbide layer, the first silicon oxycarbide layercontaining hydrogen and having a carbon content of at least about 18 at% (at least 17 at %) or a hydrogen content of at most 30 at %, and aspecific dielectric constant of at most about 3.1.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising the stepsof: preparing an underlying structure having a semiconductor substrate,a copper wiring formed above the semiconductor substrate and a siliconcarbide layer covering the copper wiring; and growing a siliconoxycarbide layer on the underlying structure by vapor deposition using,as source gas, tetramethylcyclotetrasiloxane, carbon dioxide gas andoxygen gas, a flow rate of said oxygen gas being at most 3% of a flowrate of the carbon dioxide gas.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising the stepsof: preparing an underlying structure having a semiconductor substrate,a copper wiring formed above the semiconductor substrate and a siliconcarbide layer covering the copper wiring; making hydrophilic a surfaceof the silicon carbide layer of the underlying structure by using plasmaof weak oxidizing gas which contains oxygen and has a molecular weightlarger than a molecular weight of O₂; and forming a low dielectricconstant insulating layer on the surface of the hydrophilic siliconcarbide layer, the low dielectric constant insulating layer having aspecific dielectric constant lower than a specific dielectric constantof silicon oxide.

SiOC having novel characteristics can be manufactured. Adhesion can beimproved by depositing this SiOC on an SiC layer. It is also possible toincrease a physical strength and prevent cracks and the like. Byincorporating these merits, a semiconductor device having highreliability and high performance can be provided.

The surface of an SiC layer can be made further hydrophilic. An SiOClayer having the conventional structure can be formed on the surface ofa enhanced hydrophilic SiC layer with enhanced adhesion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C show a table and graphs explaining the results ofexperiments made by the present inventors.

FIGS. 2A and 2B show a table and a graph explaining the results ofexperiments made by the present inventors.

FIG. 3 is a graph showing the results of stud-pull tests checkingadhesion of SiOC layers.

FIGS. 4A to 4D are cross sectional views of a semiconductor substrateillustrating the processes of forming a multi-layer wiring structure ofa semiconductor integrated circuit device according to an embodiment ofthe invention.

FIGS. 5A and 5B are cross sectional views of a semiconductor substrateillustrating the processes of forming multi-layer wirings according toanother object of the invention.

FIGS. 6A and 6B are cross sectional views of a semiconductor substrateillustrating the processes of forming multi-layer wirings according tostill another embodiment of the invention.

FIG. 7 is a cross sectional view of a semiconductor substrateillustrating the processes of forming a multi-layer wiring structureaccording to another embodiment of the invention.

FIG. 8 is a schematic cross sectional view showing the structure of asemiconductor integrated circuit device having a multi-layer wiringstructure.

FIG. 9 is a perspective view schematically showing the structure of aplasma CVD system.

FIG. 10 is a table showing the film forming conditions and measurementresults of samples.

FIG. 11 is a table showing the compositions of selected samples.

FIG. 12 is a graph showing infrared absorption spectra of selectedsamples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, description will be made onthe experiments made by the present inventors and the results thereofand on the embodiments of the invention.

A vapor-grown silicon oxycarbide (registered trademark CORAL) filmavailable from Novellus Systems, Inc., has a low relative dielectricfactor of about 2.9. However, it has weak adhesion to an SiC layer orthe like and is rather insufficient in terms of the physical strengthsuch as hardness and elastic constant or Young's modulus.

The present inventors have developed new CVD conditions to improve tightadhesion of a vapor-grown silicon oxycarbide film and increase thephysical strength. In the following, a conventional vapor-grown siliconoxycarbide film is called CORAL, and a vapor-grown silicon oxycarbidefilm developed by the present inventors is called TORAL or new SiOC.TORAL or new SiOC is considered having Si—O—C as its main skeleton.

FIG. 1A is a table showing growth parameters of a CORAL film and a TORALfilm. CORAL is grown by flowing, as source gas, TMCTS at 5 ml/min, O₂gas at 250 sccm and CO₂ gas at 5000 sccm, as described earlier, underthe conditions of a pressure of 4 torr, an HF power of 600 W and an LFpower of 400 W.

The present inventors have tried if the physical strength can beimproved by lowering a deposition speed. In order to lower thedeposition speed, the flow rate of the source gas TMCTS was reduced to 1ml/min or by one fifth, and the HF and LF powers were lowered to 300 Wand 200 W or by one second, respectively. The flow rate of O₂ gas wasreduced more than that of CORAL in the range of 0 to 200 sccm. The O₂gas flow was set to 0, 50, 80, 100, 120, 150 and 200 (sccm).

The deposition speed of TORAL was lowered to 300 to 350 nm/min which isabout ¼ to ⅓ that of CORAL. The density of TORAL increased apparently toabout 1.6 to 1.7 as compared to the density of about 1.4 of CORAL.

FIGS. 1B and 1C are graphs showing the physical constants of TORAL filmsdeposited in the manner described above.

FIG. 1B is a graph showing a change in hardness and elastic constant(modulus) relative to the oxygen flow rate. The abscissa of FIG. 1Brepresents an oxygen flow rate in the unit of sccm, and the ordinaterepresents hardness in the unit of GPa and the modulus in the unit ofGPa. Measurement points coupled by solid lines indicate hardness data,and measurement points coupled by broken lines indicate modulus data.White circles indicate hardness and modulus of CORAL given for thepurpose of comparison. The abscissa has no meaning for CORAL (becausethe oxygen flow rate is constant at 250 sccm).

As seen from FIG. 1B, hardness and modulus are generally constantirrespective of the O₂ flow rate, although they change more or less atthe O₂ flow rates of 100 and 120 (sccm). As compared to the hardness ofabout 2 GPa of CORAL, the hardness of TORAL increased to about 3 GPa.The elastic constant is about 13 GPa for CORAL whereas the elasticconstant for TORAL increases to about 20 GPa. TORAL increases thephysical strength greatly as compared to that of CORAL. It is thereforeexpected that the generation of cracks is suppressed. Reducing the flowrates of source gas, TMCTS and oxygen, is effective for lowering thedeposition speed and improving the physical strength.

Dependency of physical strength on the oxygen flow rate is low. From theview point of physical strength, it is considered that the flow rate ofoxygen can be decreased as desired.

FIG. 1C is a graph showing a change in the specific dielectric constantwith an oxygen flow rate. The abscissa represents an oxygen flow rate inthe unit of sccm and the ordinate represents a specific dielectricconstant. As seen from FIG. 1C, as the oxygen flow rate reduces, thespecific dielectric constant lowers. At the oxygen flow rate larger than100 sccm, particularly larger than 150 sccm, the specific dielectricconstant increases remarkably. In order to maintain the specificdielectric constant low, it is preferable to set the oxygen flow rate to150 sccm (3% of the CO₂ gas flow rate) or smaller, particularly to 100sccm (2% of the CO₂ gas flow rate) or smaller. The specific dielectricconstant is required to be 3.1 or smaller in order to satisfy thecapacitance design value of devices under the technical state of currentdevelopments. TORAL satisfying this condition corresponds to sampleshaving the oxygen flow rate of 50 sccm or the oxygen flow rate of 0. Inorder to set the specific dielectric constant to about 3.1 or smaller,it is preferable to set the oxygen flow rate to 50 sccm (1% of the CO₂gas flow rate) or smaller. The specific dielectric constants of thesesamples are approximately equal to or slightly higher than the specificdielectric constant of about 2.9 of CORAL. The hardness and modulus areincreased considerably as compared to those of CORAL, as shown in FIG.1B.

FIG. 2A is a table showing the compositions of films measured byRutherford backward scattering or the like. There exists a measurementerror of ±2%. Even if the precision is raised through averaging, anerror of ±1% may still exist. TORAL samples were made at the oxygen flowrates of 0, 50 and 150 (sccm). For the comparison purpose, measurementswere also conducted for CORAL and ESL3 which is silicon carbide (SiC)available from Novellus Systems, Inc. A vapor-grown silicon carbide filmcontains Si, C and in addition a fairly large amount of H and O, Sincesilicon carbide has Si—C as its main skeleton, H and O are expected tobe coupled to outer positions of the main skeleton.

As compared to ESL3, the silicon oxycarbide film CORAL has apparently anincreased amount of oxygen and a decreased amount of other components.Silicon oxycarbide is considered having the main skeleton Si—O—C. It canbe considered that although silicon carbide (ESL3) contains Si, O and Cat about 20%, it has substantially no Si—O—C skeleton. As compared tothe compositions of CORAL, the compositions of TORAL has an increasedamount of Si, a slightly increased amount of at least O, and a decreasedamount of H. As compared to CORAL, TORAL having the oxygen flow rate of50 sccm or smaller has carbon (C) more by about 2 at % or higher andhydrogen (H) less by about 12 at %.

The composition of carbon (C) of TORAL increases as the oxygen flow rateis lowered. An increase in the C contents may be ascribed to anincreased influence of CO₂. By considering that the oxygen flow rate ispreferably set to 50 sccm in order to realize the specific dielectricconstant of about 3.1, it is preferable that the composition of thecarbon (C) is set to about 18 at % or larger (or 17 at % or larger).According to the experiment results, the C composition is preferablyabout 18 to 21 at % (17 to 22 at %). Although it can be expected thatthe larger the C composition, the lower the specific dielectricconstant, the state that the amount of C is larger than that of Si maypose a problem of characteristics. The C composition is thereforepreferably about 25 at % (26 at %) or smaller.

The composition of hydrogen (H) is about 20 at % (21 at %) which is farlarger than about 32 at % of CORAL. Hydrogen is not an essential elementfor silicon oxycarbide, but it is the component accompanied when TMCTSis used as the source gas. Hydrogen is considered having a function ofreducing cross links by terminating the bonds of Si, C and O. The amountof hydrogen contents is therefore preferably as small as possible. Evenif oxygen is flowed at 150 sccm, the hydrogen composition exists atabout 11 at % so that it is difficult to lower the hydrogen compositionto about 11 at % or lower when the oxygen flow rate is set to 50 sccm.

FIG. 2B is a graph showing infrared absorption spectra of a CORAL filmand a TORAL film. The abscissa represents a wave number in the unit ofcm⁻¹ and the ordinate represents an absorption. Absorption, which can beconsidered being caused by Si—H near at a wave number of 2200 to 2300cm⁻¹, can be observed clearly for CORAL, whereas such absorption is assmall as it is hardly observed for TORAL. As compared to CORAL,absorption caused by C—H near at a wave number 3000 cm⁻¹ is reduced forTORAL. A decrease in Si—H and C—H may be ascribed to a reduction ofterminated bonds and an increase in bridge density (cross links). If thecross links increase, it can be expected that the physical strength suchas hardness and modulus can be improved. This expectation matches theincrease in C composition and the decrease in H composition.

Although SiC to be used as a copper diffusion preventive film ishydrophilic in strict speaking, the surface of the film is ratherwater-repellent (hydrophobic). SiC/SiOC/SiC structures having a siliconoxycarbide film sandwiched between silicon carbide films were formed andstud-pull tests using Sebastian tester were conducted.

FIG. 3 is a graph showing the stud-pull test results. The ordinaterepresents a strength applied during the stud-pull test, the strengthbeing in the unit of MPa. A sample c has a conventional CORAL layersandwiched between SiC layers. A sample s1 has a TORAL layer in place ofan SiC layer, sandwiched between SiC layers. It can be seen that thetight adhesion is improved clearly in the latter case. Although theCORAL sample had many peel-off at the interface of underlying SiC/CORAL,the TORAL sample had no peel-off at the interface.

A sample s2 has a lower SiC layer, a TORAL layer of 50 nm in thicknessformed at an HF power of 90 W on the lower SiC layer, a CORAL layerformed on the TORAL layer and an SiC layer formed on the CORAL layer. Inthis case, it cannot be said necessarily that the tight adhesion isimproved.

A sample s3 has the structure similar to that of the sample s2, but theTORAL layer was formed by raising the HF power from 90 W to 200 W. Itcan be said that the tight adhesion is improved fairly to the extentsimilar to or greater than the conventional CORAL sample. Raising the HFpower applied when the TORAL layer is formed is considered preferable inorder to improve the tight adhesion.

The SiC layer has a surface like a water repellent surface. It can beconsidered that if a silicon oxycarbide film is formed on the surfacelike a water repellent surface, the tight adhesion may be degraded. Ifthe surface of an SiC layer is changed more hydrophilic, the tightadhesion is expected to be improved. In the experiments, the surface ofan SiC layer was changed hydrophilic by CO₂ plasma. The CO₂ plasmaprocess was performed by a down-flow process of microwave excited plasmaunder the conditions of a CO₂ flow rate of 5000 sccm, a pressure of 4torr, an RF power of 100 (90 to 200) W and a process time of 5 seconds.

A sample s4 shown in FIG. 3 was formed by processing the surface of alower SiC layer with CO₂ plasma (changing the surface hydrophilic),thereafter depositing a CORAL layer and depositing an SiC layer on theCORAL layer. A strength of nearly 70 MPa or larger was obtained and itcan be said that the tight adhesion is improved apparently. Also in thiscase, peel-off at the interface SiC/CORAL was not observed.

According to the test results shown in FIG. 3, the tight adhesion isimproved most when the SiC surface is subjected to a hydrophilic processby CO₂ plasma. This may be ascribed to the underlying SiC layer surfacechanged more hydrophilic.

When the underlying SiC layer surface was processed by O₂ plasma insteadof CO₂ plasma, the tight adhesion was degraded. The O₂ plasma processingconditions were an O₂ flow rate of 500 sccm, a pressure of 2 torr, apower of 200 W and a process time of 2 seconds.

The result of the stud-pull test of a sample without a CO₂ plasmaprocess showed a strength of 55 MPa, whereas the result of the stud-pulltest of a sample with a CO₂ plasma process showed a strength of 70 MPa,indicating definite improvement on the tight adhesion. No peel-off wasobserved at the SiC/CORAL interface similar to that described above. Theresult of the stud-pull test of the sample subjected to the O₂ plasmaprocess showed a degraded tight adhesion of 45 MPa. Peel-off wasobserved mainly at the SiC/CORAL interface. This may be ascribed to thatexcessive oxidation by the O₂ plasma process degrades the tight adhesiondue to surface decomposition.

In order to perform a plasma process without excessive oxidation, it maybe preferable to use a down-flow process of microwave excited plasma orother processes.

When the oxygen flow rate is reduced to 0 to 50 sccm when a TORAL layeris formed, plasma of the source gas in a chamber contains a decreased O₂composition and a relatively increased CO₂ composition. It can beconsidered in other words that plasma of the source gas becomesapproximately CO₂ plasma. It may be considered that high tight adhesionof the TORAL film to the SiC film matches high tight adhesion of the SiCfilm subjected to the CO₂ plasma process to the CORAL film formed on theSiC film. Good results can be obtained by using plasma of gas whichcontains CO₂ and does not contain oxygen or plasma with an oxygen flowrate restricted small relative to a CO₂ flow rate.

It can be considered from these results that it is effective for tightadhesion improvement to gently oxidize the near-water-repellent or waterrepellent surface of an SiC film or the like. From the fact that O₂plasma showed bad results and CO₂ plasma showed good results, it can beconsidered preferable to process the surface by plasma of gas which hasa molecular weight larger than that of O₂ and contains oxygen. Gas ofNO₂ or the like may be used in addition to CO₂.

Studies made by the present inventors have been directed further to theconditions of forming a silicon oxycarbide film having a proper physicalstrength and a low specific dielectric constant by selecting the plasmaCVD conditions.

FIG. 9 is a schematic diagram showing the structure of a plasma CVDsystem used. A lower electrode 50 severs also as a susceptor for placingthereon six 8-inch wafers. The susceptor is provided with a transportmechanism for transporting each wafer. Six upper electrodes 51 a, 51 b,51 c, 51 d, 51 e and 51 f are disposed facing the lower electrode 50 toconstitute six pairs of diode parallel plate electrodes. These parallelplate electrodes constitute six stages S0 to S5.

The upper electrodes are connected to high frequency (HF) power sources52 a, 52 b, . . . , 52 f, respectively. The lower electrode 50 isconnected to a high frequency power source 53 having a frequency (LF)lower than the high frequency (HF). The upper electrodes also have thefunction of shower heads for supplying source gas. The lower electrodes50 contain heater blocks. When a high frequency power is supplied to allthe stages, the total high frequency power is equally divided to sixparts and supplied to the respective stages. It is also possible tosupply high frequency power selectively to a selected stage. By applyinga predetermined high frequency voltage between the lower electrode 50and a predetermined upper electrode 51, plasma can be generated above apredetermined wafer.

A transported wafer is placed on a first stage under the first upperelectrode 51 a and undergoes a proper process. Thereafter, the waferundergoes processes sequentially at a second stage S1, a third stage S2,a fourth stage S3, a fifth stage S4 and a sixth stage S5, and thereafteris ejected out. Experiment results of silicon carbide films will bedescribed which were subjected to the same process at each stage. Unlessspecifically denoted, the amounts of gas supply and high frequency powerare total values for six stages.

FIG. 10 shows the conditions and results of each experimental sample.Some samples are excluded which have a large irregularity of filmthickness. Source gas used is TMCTS of 1 ml/min, (O₂: 0 sccm) and CO₂ of5000 sccm for all samples. A deposition speed, an irregularity ofintra-wafer film thickness and a refractive index were measured bychanging a chamber inner pressure, a high frequency power HF applied tothe upper electrode and a high frequency power LF applied to the lowerelectrode. The irregularity of film thickness was measured at 49 pointsof each wafer and represented by % of a half of a difference betweenmaximum and minimum average values. There is a relation that a square ofa complex refractive index (n+ik) is equal to the complex dielectricconstant. The refractive index n is measured as a physical quantityhaving a close relation to the dielectric factor. The refractive index nis, however, measured at a frequency of light which is greatly differentfrom a frequency of an electric signal at which the dielectric constantis measured.

A sample 1 uses TORAL formed at the oxygen flow rate of 0 describedabove. The chamber inner pressure is gradually lowered at the same HFand LF powers to obtain samples 1 to 4. As the chamber inner pressure islowered, the deposition speed gradually lowers. This may be ascribed tothat as the pressure lowers, the amount of source gas supplied to thewafer reduces. As the deposition speed lowers, the irregularity of filmthickness reduces and the regularity is improved. The refractive indexgradually increases as the deposition speed lowers.

Paying attention to the sample 2 which has a relatively good regularityof film thickness, not so large an increase in refractive index and agood stability of plasma, a hardness, a modulus and a specificdielectric constant were measured. According to the experiment results,the sample 1 has the hardness of 3, modulus of about 20 GPa and specificdielectric constant of about 3.0. The hardness of the sample 3 increasesto about 4.0 and the modulus increases to about 23.6. The specificdielectric constant maintains about 3.0. It can be said that the sample3 is an excellent low dielectric constant insulating layer having anincreased physical strength and maintaining the same specific dielectricconstant, as compared to the sample 1. In the following, this novel SiOCis called SiOC-A.

For samples 5 to 9, the pressure was fixed to 3.5 torr and HF and LFpowers were raised. As both the HF and LF powers are raised, thedeposition speed gradually increases, excepting the sample 6. It appearsthat there is no definite rules of the film thickness irregularity andrefractive index. The physical properties of the samples 6 and 9 weremeasured by taking into consideration the plasma stability and the like.The sample 6 has a hardness of 3.5, a Young's modulus of 24.7 and aspecific dielectric constant of 3.2. The sample 9 has a hardness of 4.4,a Young's modulus of 30.1 and a specific dielectric constant of 3.3.Although the physical strength of the hardness and Young's modulus issuperior to that of TORAL, the application field of a low dielectricconstant insulating film may be restricted at a specific dielectricconstant of 3.2 or larger. It can be supposed that if the high frequencypower is simply raised, the specific dielectric constant increases.

For samples 10 to 14, the chamber inner pressure is fixed to 3.5 torr,the LF power applied to the lower electrode is fixed to 200 W and onlythe HF power applied to the upper electrode is raised to 600 W startingfrom 400 W. Although the sample 10 shows exceptionally a high depositionspeed and a low film thickness irregularity, the samples 11 to 14gradually increase the deposition speed as the HF power is raised. Thefilm thickness irregularity is low particularly for the samples 13 and14. It seems there is the tendency that the refractive index lowers asthe HF power is raised. The refractive index is low particularly for thesample 14. The physical properties of the sample 14 were a hardness of3.6 GPa, a Young's modulus of 23.4 GPa and a specific dielectricconstant of 3.2. Although the hardness and Young's modulus are high, thespecific dielectric constant is also high so that the application fieldof a low dielectric constant insulating layer is restricted.

For samples 15 to 18, the chamber inner pressure is fixed to 4.0 torrand the HF and LF powers are changed. Although the sample 15 is formedin the same conditions as those of the sample 1, the deposition speed isslightly high and the film thickness irregularity is reduced. This isconsidered to show a kind of variation in a process of the samecondition. For the samples 16 to 18, the HF power applied to the upperelectrode is fixed to 600 W and the LF power is changed from 0, 200 to400 W. For the sample 16, the LF power applied to the lower electrode isset to 0. The deposition speed considerably lowers to 89. The samples16, 17 and 18 show an abrupt increase in deposition speed and a reducedfilm thickness irregularity as the LF power is raised. It seems that therefractive index increases as the deposition speed increases. It can beunderstood that the LF power applied to the lower electrode greatlyinfluences film formation.

For samples 19 to 22, the chamber inner pressure is increased to 4.5torr. For the samples 19 to 21, the LF power applied to the lowerelectrode is fixed to 200 W and the HF power applied to the upperelectrode is raised from 600, 800 to 900 W. As the HF power applied tothe upper electrode is raised, the deposition speed increases. Ascompared to the sample 19, the samples 20 and 21 reduce the filmthickness irregularity considerably. The samples 19 to 21 have therefractive index lower than that of the samples 1 to 18. The physicalproperties of the sample 20 having a low film thickness irregularity andan excellent plasma stability were measured, which showed a hardness of2.0, a Young's modulus of 17.3 and a specific dielectric constant of2.85. Although the hardness of 2.0 is almost equal to that of CORAL, theYoung's modulus of 17.3 is superior to that of CORAL and the specificdielectric constant of 2.85 is lower than that of CORAL. Since thespecific dielectric constant is low and the Young's modulus is improved,this low dielectric constant insulating layer is expected to be used invarious application fields. In the following description, this novelSiOC is called SiOC-B.

For a sample 22, the LF power applied to the lower electrode is raisedby 100 W more than that of the sample 21. The deposition speed increaseslargely, and the refractive index increases although the film thicknessregularity is good.

For samples 23 and 24, the chamber inner pressure is increased furtherto 5.0 torr and the LF power applied to the lower electrode is set to200 W. The HF power applied to the upper electrode was set to 1100 W and1200 W. As the HF power is raised, although the deposition speedincreases and the film thickness irregularity increases, the refractiveindex lowers gradually.

It has been found that an insulating layer having a low specificdielectric constant can be formed by using TMCTS and CO₂ without usingoxygen. The samples 3 and 20 among others have a low specific dielectricconstant and provide excellent low dielectric constant insulatinglayers. The sample 3 is, however, associated with some instability of aplasma state so that particles are deposited on the wafer due to flowingsource gas when the plasma is being quenched or extinguished.

To avoid this, following the plasma CVD process, only CO₂ gas wassupplied to generate CO₂ plasma to terminate the plasma CVD and slightlyoxidize the CVD film surface by switching over plasma CVD to CO₂ plasmatreatment. The CO₂ plasma generation conditions are a CO₂ flow rate of5000 sccm, a pressure of 1 torr and an HF power of 150 W. Several tenthousands of particles having a diameter of 0.1 μm are deposited on awafer of the sample 3 having a diameter of 20 cm. However, by generatingCO₂ plasma at the time of plasma quenching, the number of particleshaving a diameter of 0.1 μm was able to be reduced to several hundreds,and in better conditions, to about 100 particles. In the plasma CVDsystem shown in FIG. 9, the SiOC film is deposited at six stages. TheCO₂ plasma process was performed at each stage following the depositionof the SiOC film.

The compositions of films were measured, the films including a filmSiOC-A made of the sample 3, a film SiOC-A:POX made of a film formedunder the same conditions as those of the sample 3 and subjected to CO₂plasma at the time of plasma quenching, and a film SiOC-B made of thesample 20. The composition measurement precision has an approximateerror of ±2 at %.

FIG. 11 is a table showing the compositions of the films SiOC-A,SiOC-A:POX and SiOC-B, with those of CORAL. The specific dielectricconstants are also shown. SiOC-A has the same compositions as those ofTORAL at the oxygen flow rate of 0. As compared to SiOC-A, SiOC-Breduces carbon and silicon by 3 at % and increases hydrogen by 7 at %.It appears that there exists the phenomenon different from the carboncomposition dependency of TORAL observed when the oxygen flow rate islowered. A possibility of existence of a different phenomenon cannot benegated because the pressure is set higher and the HF power is raisedmuch higher than those of SiOC-A. As compared to CORAL, the pressure andHF power are raised and the LF power is lowered.

As compared to SiOC-A, it can be considered that cross links are reduceddue to an increase in hydrogen and the mechanical strength is lowered.However, as compared to CORAL, the hydrogen contents are remarkablysmall (about 5 at %) and the carbon contents are large by about 2 at %.The measured carbon content values were 17.8 and 17.9. When themeasurement errors are considered, these measurement values fall in theabove-described preferable range of about 18 at % or higher (17 at % orhigher). It can be said that the carbon contents are larger than thoseof CORAL by about 1 at % or larger. The mechanical strength is higherthan that of CORAL and the specific dielectric constant of 2.85 is lowerthan that of CORAL.

The hydrogen composition is about 27 at % which is apparently lower thanabout 32 at % of CORAL. This is considered corresponding to themechanical strength far more excellent than CORAL. Silicon oxycarbidecan therefore be realized which has the hydrogen composition of about 27at % or smaller (28 at % or smaller) and is excellent in the mechanicalstrength and has a specific dielectric constant of about 3.1 or smaller.Low dielectric constant silicon oxycarbide is expected to be realized ata hydrogen composition of about 29 at % or smaller (30 at % or smaller),which silicon oxycarbide has a mechanical strength superior to that ofCORAL and a specific dielectric constant of about 3.1 or smaller.

SiOC:POX is obtained by growing SiOC-A and thereafter processing theSiOC-A surface by a CO₂ plasma process for 2 seconds at each of the sixstages shown in FIG. 9. The compositions of SiOC-A:POX is considered thesame as those of SiOC-A. The measured compositions are considerablydifferent from those of SiOC-A. This may be ascribed to absorption ofwater contents or the like in the oxidized surface layer afterSiOC-A:POX is exposed to the atmospheric air. Although the specificdielectric constant increases, the number of particles on the wafersurface is reduced greatly.

FIG. 12 is a graph showing spectra of infrared absorption of SiOC-A andSiOC-B, being compared to infrared absorption of a reference (CORAL).The abscissa represents a wave number in the unit of cm⁻¹ and theordinate represents an absorption. As compared to the reference Ref, C—Habsorption reduces near at the wave number of 3000 cm⁻¹. Similarly, C—Habsorption reduces also near at the wave number of 1270 cm⁻¹.Conversely, Si—CH₂—Si absorption near at 1360 cm⁻¹ increases more thanthat of the reference Ref. It can be understood from these absorptionspectra that as compared to the reference Ref, SiOC-A and SiOC-B have anincreased umber of C—H bonds and a decreased number of cross links. Itcan be considered that an increase in cross links improves the physicalstrength.

FIGS. 4A to 4D are cross sectional views illustrating a manufacturemethod for a semiconductor integrated circuit device according to anembodiment of the invention.

As shown in FIG. 4A, after an element isolation region, an elementstructure including MOS transistors, and the like are formed on asilicon substrate 100, a phosphosilicate glass (PSG) layer 11 is formedby vapor deposition to a thickness of about 1.5 μm at a substratetemperature of 600° C. The surface of the PSG layer 11 is planarized bychemical mechanical polishing (CMP) and thereafter a resist layer isdeposited on the surface of the PSG layer 11 to form a resist patternhaving electrode lead openings. By using the resist pattern as a mask,the PSG layer 11 is etched to form via holes exposing the contact areason an underlying region. The resist pattern is removed thereafter. Aftera barrier layer such as Ti or the like is formed, a W layer is formed byCVD or the like to bury the electrode lead via holes. The W layer andthe like deposited on the PSG layer 11 are removed by CMP to formtungsten plugs 12.

An SiC layer 14 as an etch stopper layer is formed to a thickness ofabout 70 nm, covering the tungsten plug 12, the etch stopper layerhaving an oxygen shielding function and being made of ESL3 (registeredtrademark) of Novellus Systems, Inc. Next, a silicon oxycarbide (SiOC)layer 15 of TORAL is deposited to a thickness of 550 nm. The oxycarbidelayer 15 having improved tight adhesion and physical strength istherefore formed on the SiC layer 14.

An SiC layer 17 functioning as a middle stopper layer is deposited onthe surface of the SiOC layer 15 to a thickness of about 30 nm, the SiClayer being made of ESL2 (registered trademark) of Novellus Systems,Inc. An SiC layer 18 of TORAL is deposited on the SiC layer 17 to athickness of about 370 nm. The SiOC layer 18 has also improved tightadhesion to the SiC layer 17 and having improved physical strength. Anantireflection film ARC1 is formed on the surface of the SiC layer 18.

On this antireflection film ARC1, a photoresist layer PR1 having a viahole opening pattern is formed. By using the photoresist pattern PR1 asan etching mask, the antireflection film ARC1, SiOC layer 18, SiOC layer17 and SiOC layer 15 are etched.

As shown in FIG. 4B, the photoresist pattern PR1 is removed and aphotoresist layer PR2 having a wiring pattern opening is newly formed. Afiller F is buried in a via hole already formed. The filler F is made ofresist material removed with photosensitivity. By using the photoresistlayer PR2 having the wiring pattern opening as an etching mask, theantireflection film ARC1 and SiOC layer 18 are etched. Thereafter, thephotoresist pattern PR2 and filler F are removed and the exposed SiClayers 17 and 14 are selectively etched to thereby form a dual damascenetrench.

As shown in FIG. 4C, a TaN barrier layer 19 a of about 30 nm inthickness and a Cu seed layer 19 b of about 30 nm in thickness areformed by sputtering on the inner surface of the dual damascene trench.The Cu seed layer 19 b is used for plating Cu thereon. On the surface ofthe Cu seed layer 19 b, a Cu layer 19 c is plated. In this manner, thedual damascene trench is filled with copper wiring. An unnecessary Culayer and the like deposited on the SiOC layer (including theantireflection film ARC1) are removed by CMP. In this case, theantireflection film ARC1 can be used as a stopper. The antireflectionfilm is also removed by the CMP or etching.

As shown in FIG. 4D, an SiC layer 24 of ESL3 (registered trademark) ofNovellus Systems, Inc. is formed to a thickness of about 70 nm, coveringthe Cu wiring 19. This SiC layer has a function of a copper diffusionpreventive film.

An SiOC layer 25 of TORAL similar to that described earlier is formed toa thickness of about 550 nm as an interlayer insulating film for anupper wiring. On this SiOC layer 25, an SiC layer 27 is formed to athickness of about 30 nm, and an SiOC layer 28 of TORAL is formed to athickness of about 370 nm on the SiC layer 27. On the surface of theSiOC layer 28, an antireflection film ARC2 is formed to complete alamination structure. By performing the processes similar to those shownin FIGS. 4A, 4B and 4C, a dual damascene wiring is formed buried in theinterlayer insulating films 24, 25, 27 and 28.

If necessary, similar processes are repeated to form the necessarynumber of wiring layers. An interlayer insulating film of silicon oxideis formed and aluminum (Al) pads are formed thereon. With thisstructure, a wiring having a capacitance of 180 fF/mm was able to beformed, for example, in the second wiring layer. Whether there is anyfilm peel-off was checked by repeating heat treatment for 30 minutes at400° C. five times. Film peel-off was not observed at all.

Heat cycle tests were conducted for a multi-layer wiring structure madeof pairs of an SiC layer and a conventional silicon oxycarbide film (ofCORAL (registered trademark) of Novellus Systems, Inc.) formed on theSiC layer and having the same film thickness as that of the embodimentstructure. Peel-off was observed between the underlying SiC layer andthe CORAL layer.

Other novel silicon oxycarbide films may also be used.

As a modification, a multi-layer structure was formed by using an SiOC-Alayer having a thickness of 350 nm as the silicon oxycarbide layers 15and 25 and an SiOC-A layer having a thickness of 550 nm as the siliconoxycarbide layers 18 and 28. The SiOC-A forming conditions are a TMCTSflow rate of 1 ml/min, a CO₂ flow rate of 5000 sccm, a pressure of 3.5torr, an HF power of 300 W and an LF power of 200 W. Also with thismulti-layer structure, film peel-off was not observed at all even ifheat treatment for 30 minutes at 400° C. was repeated five times. Thecapacitance of the second wiring layer was about 180 fF/mm. At theinterface between an oxycarbide layer made of CORAL of Novellus Systems,Inc. and the underlying SiC layer, peel-off was observed after heatcycle tests.

When SiOC-A is manufactured, the chamber inner pressure is relativelylow, 3.5 torr, and plasma is likely to become unstable. Particles arelikely to be formed at the time of plasma quenching. At the time ofplasma quenching, the supply of source gas is stopped and CO₂ gas isintroduced to generate CO₂ plasma for 2 seconds. It is possible in thismanner to prevent particles from being generated. Although there is apossibility that a specific dielectric constant increases slightly, aninsulating layer without particles can be formed.

In the above-described modification, after each SiOC-A film is formed,in six-stage SiOC deposition process, the surface of the SiOC film wasprocessed for 2 seconds at each plasma quenching by using CO₂ plasmagenerated under the conditions of a CO₂ flow rate of 5000 sccm, apressure of 1 torr and an HF power of 150 W. In other words, the SiOCfilms 15, 18, 25, and 28 are formed of SiOC-A:POX. Also in this case,film peel-off was observed not at all after repeating heat treatment for30 minutes at 400° C. for five times. The capacitance of the secondwiring layer measured was about 180 fF/mm.

SiOC-B may also be used. For example, in the modification, as thesilicon oxycarbide layers 15, 18, 25 and 28, a silicon carbide layer ofSiOC-B was used which was manufactured under the conditions of a TMCTSflow rate of 1 ml/min, a CO₂ flow rate of 5000 sccm, a pressure of 4.5torr, an HF power of 800 W and an LF power of 200 W. The capacitance ofthe second wiring layer measured was about 180 fF/mm. Film peel-off wasobserved not at all after repeating heat treatment for 30 minutes at400° C. for five times.

When SiOC-B is manufactured, the chamber inner pressure is relativelyhigh so that plasma can be made stable and the generation of particlescan be suppressed. In addition, the specific dielectric constant can belowered further, which is effective for reducing the capacitance betweenwirings.

In the above embodiment, the interlayer insulating film other than theetch stopper layer (copper diffusion preventing film) is made of thesilicon oxycarbide layer of TORAL. The TORAL layer may be used as anintermediate layer combined with other layers. The material of the TORALlayer may be silicon oxycarbide formed at an oxygen flow rate of 50 to 0sccm.

FIGS. 5A and 5B are cross sectional views illustrating a wiring formingprocess for a semiconductor integrated circuit device according toanother embodiment of the invention.

As shown in FIG. 5A, on the surface of a silicon substrate 10, aninterlayer insulating film 11 and a lower wiring 12 respectively made ofPSG similar to the embodiment described above are formed. An etchstopper SiC layer 14 is formed to a thickness of about 50 nm by usingESL3 (registered trademark) of Novellus Systems, Inc, the SiC layercovering the surface of the lower level wiring 12.

On the SiC layer 14, an SiOC layer 15 x of TORAL is deposited to athickness of about 50 nm. As described earlier, this SiOC layer 15 x hasimproved tight adhesion to the underlying SiC layer. On the SiOC layer15 x of TORAL, an SiOC layer 15 y of CORAL similar to a conventionalexample is formed to a thickness of about 500 nm. Next, an SiC layer 17as a middle stopper is formed to a thickness of about 30 nm by usingESL2 (registered trademark) of Novellus Systems, Inc. On this SiC layer,an SiOC layer 18 x of TORAL is formed as a liner to a thickness of about50 nm. On the SiOC layer 18 x of TORAL, an SiOC layer 18 y of CORAL isformed to a thickness of about 320 nm. On the SiOC layer 18 y, anantireflection film ARC1 of SiN or the like is formed.

Thereafter, similar to the processes shown in FIGS. 4A to 4C, a dualdamascene trench is formed by photoresist mask forming and etchingprocesses.

As shown in FIG. 5B, a TaN layer and a Cu seed layer are formed bysputtering on the inner surface of the dual damascene trench, and a Culayer 19 is plated on the Cu seed layer. By planarizing the surface ofthe Cu layer by CMP, a dual damascene copper wiring 19 is formed. An SiClayer 24 as a copper diffusion preventive layer is formed covering thecopper wiring 19, the SiC layer having a thickness of 70 nm and beingmade of ESL3 of Novellus Systems, Inc.

Processes similar to the above processes are repeated to form a desirednumber of wiring layers. The capacitance of, e.g., the second wiringlayer of the multi-layer structure constructed as above was about 180fF/mm.

Whether there is any film peel-off was observed by repeating heattreatment for 30 minutes at 400° C. five times. Film peel-off wasobserved not at all.

Other novel SiOC materials may be used in place of TORAL. A siliconoxycarbide layer having a thickness of 50 nm and made of SiOC-A was usedas the SiOC layers 15 x and 18 x. The parasitic capacitance of thesecond wiring layer of the multi-layer structure was about 180 fF/mm.Film peel-off was observed not at all after repeating heat treatment for30 minutes at 400° C. five times.

It has been found that the tight adhesion can be improved by interposingan SiOC layer of TORAL or SiOC-A between the SiOC layer of CORAL and theSiC layer as the underlying etch stopper layer.

In this embodiment, on the surface like a water repellent surface of theSiC layer having the copper diffusion preventive function, the SiOClayer of TORAL is formed to form a multi-layer wiring structure havingimproved tight adhesion between the SiC and SiOC layers.

Tight adhesion can be improved also by the surface processing of an SiClayer.

FIGS. 6A and 6B are cross sectional views of a silicon substrateillustrating the process of forming a multi-layer wiring structure of asemiconductor integrated circuit device according to a furtherembodiment of the invention. Similar to the embodiment described above,an interlayer insulating film 11 and a lower wiring 12 are formed on thesurface of a semiconductor substrate 10. An SiC layer 14 having athickness of about 70 nm and made of ESL3 (registered trademark) ofNovellus Systems, Inc. is formed covering the surface of the lowerwiring 12. The surface of the SiC layer 14 is subjected to a processusing CO₂ plasma. By using the CVD system shown in FIG. 9, the CO₂process was performed at the first stage S0. The process conditions werea CO₂ flow rate of 5000 sccm, a pressure of 4 torr, an RF power of 200 Wand a process time of 5 seconds. It can be considered that this plasmaprocess forms a hydrophilic surface 14 x on the surface of the SiC layer14.

On the hydrophilic surface of the SiC layer 14, an SiOC layer 15 y isformed to a thickness of about 550 nm by using CORAL (registeredtrademark) of Novellus Systems, Inc. On this SiOC layer 15 y, an SiClayer 17 as a middle stopper is formed to a thickness of about 30 nm byusing ESL2 (registered trademark) of Novellus Systems, Inc. The surfaceof the SiC layer 17 is processed by CO₂ plasma, similar to thatdescribed before, to form a hydrophilic surface 17 x. On thishydrophilic surface 17 x, an SiOC layer 18 y of CORAL of NovellusSystems, Inc. is formed to a thickness of about 370 nm. On the surfaceof the SiOC layer 18 y, an antireflection film ARC1 of SiN or the likeis formed.

Thereafter, photolithography, etching and the like are performed in amanner similar to the above-described embodiment to form a dualdamascene trench.

As shown in FIG. 6B, a TaN layer and a Cu seed layer are formed on theinner surface of the dual damascene trench by sputtering to a thicknessof about 30 nm, respectively. A Cu layer is plated on the Cu seed layer.An unnecessary wiring layer on the surface of the SiOC layer 18 y isremoved by CMP or the like to complete a dual damascene copper wiring19. An SiC layer 24 as a copper diffusion preventive layer is formedcovering the copper wiring 19, to a thickness of 70 nm by using ESL3 ofNovellus Systems, Inc.

Similar to the above-described embodiment, the necessary number ofwiring layers is formed by repeating similar processes. The capacitanceof, for example, the second wiring layer of the multi-layer structureconstructed as above was about 180 fF/mm. Film peel-off was observed notat all after repeating heat treatment for 30 minutes at 400° C. fivetimes.

In the multi-layer wiring structure, it is desired in some cases that asthe material of the interlayer insulating film for lower wiring layershaving a high wiring density, an organic insulating film (e.g., SiLK(registered trademark) having a specific dielectric constant of about2.6) is used in place of SiOC having a specific dielectric constant ofabout 2.9 to 3.1.

FIG. 7 is a cross sectional view showing the structure of a multi-layerwiring structure according to another embodiment of the invention. Aftera necessary structure is formed on a silicon substrate 100, a PSG layer11 having a thickness of about 1.5 μm is formed and a tungsten plug 12is buried in the PSG layer 11.

Covering the surface of the W plug 12, an SiC layer 21 is deposited to athickness of about 30 nm. On this SiC layer, an organic insulating layer22 (made of SiLK-J150 (registered trademark of the Dow ChemicalCompany)) is formed to a thickness of about 450 nm. The surface of theorganic insulating film 22 is covered with a silicon oxide layer 23having a thickness of about 100 nm. This lamination structure formsfirst interlayer insulating layers 21, 22 and 23.

A wiring groove is formed through the first interlayer insulating layersand a copper wiring 34 is buried therein. After the surface of thecopper wiring 34 is planarized, an SiC layer 36 of about 50 nm inthickness, an organic insulating layer 37 (made of SiLK-J350 (registeredtrademark of the Dow Chemical Company)) of about 450 nm in thickness anda silicon oxide layer 38 of about 100 nm in thickness are formed. On thesurface of the silicon oxide layer 38, a hard mask layer HM of SiN isformed to a thickness of about 50 nm.

A dual damascene trench is formed by using a photoresist mask and thepattern of the hard mask HM. After the dual damascene trench is formed,a barrier metal layer and a seed layer are formed by sputtering, and aCu layer is plated to bury the dual damascene trench and form a dualdamascene Cu wiring 29. The hard mask layer HM may be removed during CMPof planarizing the surface of the dual damascene wiring 29.

Covering the surface of the dual damascene wiring 29, an SiC layer 14having a thickness of about 70 nm is formed by using ESL3 (registeredtrademark) of Novellus Systems, Inc. On the SiC layer 14, an SiOC layer15 of TORAL Is formed to a thickness of about 350 nm. On the surface ofthe SiOC layer, an SiC layer 17 of about 30 nm in thickness and an SiOClayer (Toral layer) 18 of about 550 nm in thickness are formed.

By photolithography and etching, a dual damascene trench similar to thatdescribed above is formed, and a copper wiring is buried therein. Byrepeating similar processes, a fourth wiring layer can be formed on thethird wiring layer by using an SiOC layer as an interlayer insulatinglayer. Wiring layers can be stacked as necessary.

Heat treatment for 30 minutes at 400° C. was repeated five times for themulti-layer wiring structure formed in the above manner. No filmpeel-off was observed.

Other novel SiOC layers may be used in place of TORAL. For example, theSiOC layers 15 and 18 of the above-described structure were formed byusing SiOC-B. The film forming conditions are the same as thosedescribed above. Film peel-off was observed not at all after repeatingheat treatment for 30 minutes at 400° C. five times.

Large thermal stress is considered to be applied to the boundary regionbetween the organic insulating layer 27 having a large thermal expansioncoefficient and the SiOC layer 15 having a relatively small thermalexpansion coefficient. However, no crack was formed in the thirdinterlayer insulating film.

When an SiOC layer of CORAL was used in place of the novel SiOC layer,peel-off was observed at the interface between the SiC layer and theSiOC layer of CORAL after similar heat cycle tests, and crack was formedwhich is supposed resulting from the third layer wiring layer.

When the number of layers of a multi-layer wiring structure increases,various types of interlayer insulating films can be used depending uponthe type of each wiring layer.

FIG. 8 is a schematic diagram showing the structure of a semiconductorintegrated circuit device having a multi-layer wiring structure. Formedon the surface of a silicon substrate 1 are an element isolation region2 by shallow trench isolation, a gate electrode 3 on the active regionsurface and a MOS transistor structure. A PSG layer 4 is formed buryingthe gate electrode 3 and a W plug 5 is buried in the PSG layer. Asilicon oxide layer 6 is formed on the surface of the PSG layer and avia conductor 7 is buried in the silicon oxide layer.

On the silicon oxide layer 6, a first interlayer insulating film IL1made of organic insulator is formed and a copper wiring W1 is buriedtherein. On the first interlayer insulating film IL1, a secondinterlayer insulating film IL2, a third interlayer insulating film IL3and a fourth interlayer insulating film IL4 are formed by using organicinsulator. Copper wirings W2, W3 and W4 are buried in the respectiveinterlayer insulating films.

On the fourth wiring layer, an interlayer insulating film IL5 of SiOC isformed and a copper wiring W5 is buried therein. On the fifth interlayerinsulating film IL5, a sixth interlayer insulating film IL6, a seventhinterlayer insulating film IL7 and an eighth interlayer insulating filmIL8, of similar structure as the fifth interlayer insulating film, aresequentially stacked and copper wirings W6, W7 and W8 are buriedtherein.

An interlayer insulating film IL9 of silicon oxide is formed coveringthe eighth copper wiring W8, and a copper wiring W9 is buried therein.On the interlayer insulating film, an interlayer insulating film IL10 ofsilicon oxide and a copper wiring W10 are formed, which are covered withan interlayer insulating film IL11 a of silicon oxide. In the interlayerinsulating film IL11 a, via conductors are embedded, and then coveredwith another interlayer insulating film IL11 b. openings for pads areformed through the interlayer insulating film IL11 b, and aluminum padsPD (and upper most wirings) are formed on the via conductors embedded inthe interlayer insulating film IL11. A protective film PS is formedcovering the pads PD.

In this multi-layer wiring structure, the organic interlayer insulatingfilms are used for the first to fourth wirings having the narrowestwiring space, the SiOC interlayer insulating films are used for thefifth to eighth wiring layers, and the silicon oxide layers are used forthe ninth to eleventh interlayer insulating films. Proper interlayerinsulating films are selected depending upon the wiring space so thatthe multi-layer wiring structure can be formed which has highreliability and high performance.

The present invention has been described in connection with thepreferred embodiments. The invention is not limited only to the aboveembodiments. For example, the number of wiring layers can be determinedas desired. Material other than Cu may be used as the wiring material.If a higher specific dielectric constant is permitted, a TORAL layerhaving a specific dielectric constant of about 3.1 or higher may also beused. It will be apparent to those skilled in the art that other variousmodifications, improvements, combinations, and the like can be made.

We claim:
 1. A method of manufacturing a semiconductor device comprising: preparing an underlying structure including a semiconductor substrate, a copper wiring formed above the semiconductor substrate and a first silicon carbide layer covering said copper wiring; growing a first silicon oxycarbide layer on the underlying structure by vapor deposition using, as source gas, tetra methylcyclotetrasiloxane, carbon dioxide gas and oxygen gas, a first flow rate of the oxygen gas being at most 3% of a flow rate of the carbon dioxide gas; growing a second silicon oxycarbide layer on the first silicon oxycarbide layer by vapor deposition under a different condition from the condition of growing the first silicon oxycarbide layer; growing a third silicon oxycarbide layer above said second silicon oxycarbide layer by vapor deposition using, as source gas, tetra methylcyclotetrasiloxane, carbon dioxide gas and oxygen gas, a second flow rate of said oxygen gas being at most 3% of a flow rate of the carbon dioxide gas; growing a fourth silicon oxycarbide layer on the third silicon oxycarbide layer by vapor deposition under a different condition from the condition of growing the third silicon oxycarbide layer; forming a via hole in the first silicon oxycarbide layer and the second silicon oxycarbide layer; forming a trench, which is connected to the via hole, in the third silicon oxycarbide layer and the fourth silicon oxycarbide layer; and forming a conductive layer in the via hole and the trench.
 2. The method of manufacturing a semiconductor device according to claim 1, wherein the second silicon oxycarbide layer is grown by the vapor deposition using, as source gas, tetra methylcyclotetrasiloxane, carbon dioxide gas and oxygen gas.
 3. The method of manufacturing a semiconductor device according to claim 1, wherein the first flow rate of said oxygen gas is 0%.
 4. The method of manufacturing a semiconductor device according to claim 1, further comprising: after growing the first silicon oxycarbide layer, oxidizing a surface of the first silicon oxycarbide layer with plasma of 0 containing gas.
 5. The method of manufacturing a semiconductor device according to claim 4, wherein the 0 containing gas includes at least one of CO₂ and NO₂.
 6. The method of manufacturing a semiconductor device according to claim 1, further comprising forming a silicon carbide layer on the second silicon oxycarbide layer before forming the third silicon oxycarbide layer.
 7. The method of manufacturing a semiconductor device according to claim 6, wherein the via hole is formed in the third silicon oxycarbide layer, the fourth silicon oxycarbide layer and the silicon carbide layer. 